Stockholders' Equity - Public Offerings (Details) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended
	Sep. 22, 2017	Dec. 19, 2016	Sep. 30, 2015	Sep. 23, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity
Gross proceeds from September 2017 public offering					$ 80,000
Gross proceeds from December 2016 financing						$ 24,822
Gross proceeds from initial public offering							$ 106,088
Public offering | Ordinary Shares
Stockholders' Equity
Number of shares sold	9,411,765
Shares issued price per share	$ 8.50
Gross proceeds from September 2017 public offering	$ 80,000
Proceeds from sale of stock, net of underwriting discounts, commissions and offering expenses	$ 73,300
December 2016 Financing | Common Stock
Stockholders' Equity
Number of shares sold		588,127
Gross proceeds from December 2016 financing		$ 24,800
Proceeds from sale of stock, net of underwriting discounts, commissions and offering expenses		$ 20,600
IPO, including Over-Allotment Option
Stockholders' Equity
Gross proceeds from initial public offering			$ 106,100
Proceeds from sale of stock, net of underwriting discounts, commissions and offering expenses			$ 92,400
IPO, including Over-Allotment Option | Common Stock
Stockholders' Equity
For aggregate number of ADS shares issued, the aggregate number of common shares represented			1,035,000
IPO, including Over-Allotment Option | ADS
Stockholders' Equity
Number of shares sold			10,350,000
IPO | Common Stock
Stockholders' Equity
For aggregate number of ADS shares issued, the aggregate number of common shares represented				900,000
Number of common shares represented by each ADS share				0.1
IPO | ADS
Stockholders' Equity
Number of shares sold				9,000,000
Shares issued price per share				$ 10.25
Over-Allotment Option | Common Stock
Stockholders' Equity
For aggregate number of ADS shares issued, the aggregate number of common shares represented			135,000
Over-Allotment Option | ADS
Stockholders' Equity
Number of shares sold			1,350,000
Shares issued price per share			$ 10.25